Space charge grid electron beam amplifier with dual outputs



Oct. 21, 1958 T. G. MIHRAN ETAL 2,357,480 SPACE CHARGE GRID ELECTRON BEAM AMPLIFIER WITH DUAL OUTPUTS Filed March 27, 1953 Thei Attorney.

SPACE CHARGE GRID ELECTRON BEAM AMPLIFIER WITH DUAL OUTPUTS Theodore G. Mihran, Schenectady, and Norman T: Lavoo,

Watervliet, N. Y., assignors to General Electric Company, a corporation of New York Application March 27, 1953, Serial No. 345,111

4 Claims. (Cl. 179-171) This invention relates to high frequency translating apparatus and has particular reference to a dual output amplifier.

Electron discharge devices of the type having space charge control grids, such devices being exemplified by the familiar triode, are often employed as amplifiers in high frequency ranges with the device electrodes usually being arranged in closely spaced parallel planes to minimize transit time effects. While there are particular advantages to be gained from the use of space charge con '01 devices as compared to velocity modulation devices utilizing transit time effects, such as the relatively high perveance whereby high currents can be handled for a given signal voltage and the relatively wide band width, under certainconditions not all of the available energy can be extracted from the electron stream of the device. This is likely to occur when the input signal is very weak and the resulting density modulation of the electron stream is incomplete or when the output circuit impedance is too low to extract all the available energy.

It is, therefore, an object of our invention to provide means for deriving additional output energy from a high-frequency space charge control discharge device amplifier.

It is another object of our invention to provide a high frequency amplifier apparatus having a dual output system for greater power output.

It is a further object of our invention to provide means for more fully utilizing the energy of. the space charge modulated electron stream of a high frequency discharge device amplifier.

Briefly, in accordance with our invention, a space charge control device operating in a high frequency amplifier circuit is modified to permit the electron stream to pass through the anode and a drift space following the anode. When energy is extracted from the electrons in the first or grid-anode output gap, the electron stream is velocity modulated. Under the conditions previously mentioned, namely very low signal input level or an output resonator whose resonant impedance is much lower than the electron stream impedance, the electron stream is thereby usefully velocity modulated. After drifting through the drift space, it becomes density modulated and available for excitation of a second output resonator. Thus the electron stream, which is ordinarily discarded at the anode, yields an additional power output without an increase in the direct current or radio frequency power input.

The features of my invention which I believe to be novel are set forth with particularly in the appended ZhhSiAdd quency amplifying apparatus embodying our invention.

Referring now to the drawing, a high frequency electron discharge device 1 is illustrated therein of the type.

other electron permeable grid-like electrode 7. -T he various electrodes are preferably disk-shaped with the outer portion or periphery thereof serving as a terminal or external electrode contact. The envelope .8 is provided by a number of hollow cylindrical insulators which serve to space adjacent electrodes. These spacer rings are suitably sealed to the electrodes and the completed assembly is evacuated.

Discharge device structures generally similar to that herein described are disclosed in a copending application Serial No. 345,112, filed March 27, 1953, now abandoned, by Theodore G. Mihran and assigned to the assignee of the present invention. There a combined space charge control and velocity modulation translating means is broadly claimed and described. The present application relates to a particular of the foregoing copending application.

An input circuit 9 is connected between the cathode 2 and the grid 4 and an output circuit 10 is connected between the grid 4 and permeable anode 5 to enable the device, so far as these electrodes are concerned, to operate as a conventional grounded grid amplifier in which the control grid is common to the input and output circuits.

Accordingly an input section of a concentric conductor transmission line has its outer conductor 11 coupled at one end to the external periphery of the grid electrode 4 and its inner conductor 12 connected at the corresponding end to the cylindrical terminal of the cathode 2 to provide the input circuit 9. The space charge control grid 4 is provided with a negative direct current voltage bias with respect to the cathode by means of a battery 13 arranged to be effectively connected between the outer and inner conductors 11 and 12. The cathode is also provided with a relatively large negative potential with respect to ground by means of a battery 14 having its negative terminal connected to the cathode conductor and its positive terminal grounded.

A particularly convenient means for providing direct current connections to the cathode is combined with a double stub input tuner comprising two short-circuiting tuning stubs 15 and 16, each of which has its outer conductor capacitively coupled to the outer conductor 11 of the input transmission line and its inner conductor extending through the outer transmission line conductor to engage the inner input conductor 12. A thin mica washer connect their inner and outer conductors, thus enabling direct current cathode connections to be made to the outer stub conductors. The plungers are positioned to match the impedance of the input signal source with that of the discharge device. The stub tuner in itself is conventional in design. In addition, the center conductor of one of the tuning stubs is preferably made hollow in modification 1 3 order that a heater conductor 17 may be bfaiigfif out for external heater connections thereto.

A source of high frequency signals to be amplified is accordingly coupled to the input circuit 9, the concentric line inputcircuit having its'en'd port-ton: I8 opposite the discharge device tapered to match size of the concentric conductor transmission line from the input signal source. Various other known input 'irc-uit snare tures or resonators may be substituted if desired:

The first output resonator 10 comprises a concendie conductor line section having the outer conductor 21 of the input circuit as its inner conductor and a conductor 19 coupled at one end to the periphery of the electron permeable anode 5 as its outer conductor. This gridanode output circuit is terminated by a slidable plunger 129' whose axial position is adjusted to tune the resonator to the desired frequency. The plunger 20 is of a type having a by-pass insulator, such as a mica ring, between the respective sets of contact fingerscontactin'g the inner and outer resonator conductors in order to maintain direct current insulation between the grid and anode.

An output coupling means 21 for coupling energy from the grid-anode resonator to a desired load may suitably take the form of a concentric conductor transmission line section having its outer conductor connected to the outer conductor 19'of the first output resonator and its inner conductor extending therethrough and capacitively coupled to the inner or grid conductor 11.

However, as previously mentioned, not all of the available alternating current energy may be extracted from the electron stream as it passes across the interaction gap between the gridand anode to excite that resonator. This is especially likely to occur when the input signal is so weak so as to incompletely modulate the electron beam or when the loaded resonator impedance is too low to match the effective beam impedance. Under these conditions the electrons of the electron stream do not give up all of their available energy to the alternating electric fields set up across the output gap betw'een the electrodes.

In the process of transferring energy to the output resonator, however, the electron stream is velocity modulated. That is, when an electron of the electron stream is faced with a decelerating electric field between the grid and anode, it must do work against that field. In doing so .part of its kinetic energy is transferred to the electric field and the. electron itself su'fiers a decreased velocity. The opposite occurs with respect to electrons which are accelerated by the grid-anode electric fields. When the electron stream has not been completely density modulated by the space charge control means nor completely decelerated in exciting the output circuit, it may still be usefully modulated for further translation of the remaining beam energy into alternating currentenergy.

The electrons passing the anode are velocity modulated, and as they pass through the field-free region defined by the cylinder 6, they are bunched or grouped in accordance with their velocity variations. The slow electrons' corresponding to a particular modulation cycle at' the input frequency, fall behind and the' accelerated electrons catch up to form a bunch which represents density modulation of the electron stream. Accordingly, upon emergence of the electrons from the drift tube 6 the stream is so bunched that it excites an output resonator having its excitation gap positioned along the electron path. In this case, the excitation gap is between thegrid-like electrode 7 at the exit end of the drift tube and'the collector 3.

The second output resonator 22 preferably takes the form of a concentric conductor transmission line section having its inner conductor 23 connected at one end to the collector electrode 3 and its outer conductor 24 con nected at the same end to the eriphery of the grid-like electrode The length of the line section and hence its resonant frequency is adjusted by the position of a short= circuiting sliding plunger 25'. This lunger also electri cally connects the collectorto the drift inseam to the grid-lire electrodes at either end of the drift tube, B'y

grounding the outer conductor of the second output.

resonator, the grid-like electrodes 5 and 7 as well as the drift tube 6 and the collector 3 are placed at a positive potential with respect to the cathode by the battery 14.

A second output coupling means 26, suitably corresponding in form to the first output coupling means 21 is employed to extract energy from the second or catcher resonator. In way further energy is extracted from the electron stream with the end result that greater gain and efiiciency are obtained. The output energy extracted outputs without interaction therebet'we'e'n may be em-,,

ployed. A further increase in power gain may also be obtained by feedback coupling from either output. 7

While the present invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

Whatwe claim as new and desire to secure by Letters Patent of the United States is:

1; A dual output electron discharge device of the type employing an accelerated electron stream comprisr ing a cathode for generating the electron stream, input means coupling a high frequency signal with the stream including an apertured space charge control electrode immediately adjacent said'catho'de for density modulating said stream, a first output means adjacent said inputnieans including an apertured'electrode spaced from said space charge control electrode and insulated therefrom with respect to direct current voltages and maintained at a positive direct current voltage with respect to said cath ode for accelerating said stream, an output circuit means coupled to said first output means for deriving high frequency energy from said electron stream in accord: ance with the high frequency voltage produced across said first output means, said first output means also velocity modulating said stream, means providing adrift space surrounding said electron stream following said first output means to promote bunching of said stream; an anode spaced from the exit e'n'def said drift space,

and a second output means coupled-with said electron beam including a pair of spaced electrodes positioned between said exit end and said anode for deriving electromagnetic energy from said bunched electron stream.

2. A high frequency amplifier having an electron emissive cathode and a collector electrode having an electron path between them, means for applying a direct current potential to accelerate a stream of electrons between said.

cathode and collector electrode, input resonator means including a control grid positioned near said cathode for space charge modulating the electron stream with a high modulation imposed by the extraction of energy there-v from, a second output resonator following said drift space for extracting further energy from the electron stream in accordance with the velocity modulation thereof produced by the first output means, and output cou-.

pling means coupledto said first and second output resonators. l

3. A high frequency amplifier having a cathode "and;

a collector electrode having: an electron stream path' between them, means for applying a direct current potential for accelerating an electron stream along said path, an input resonator having an excitation gap defined by said cathode and an apertured control electrode spaced along said stream from said cathode, means for upplying a high frequency input signal to said input resonator to density modulate the electron stream by space charge control, a first output resonator having an excitation gap spaced further along said path for extracting energy from said stream in accordance with the density modulation thereof and including an apertured accelerating electrode maintained at a positive direct current voltage with respect to said control electrode, means for coupling energy from said first output resonator to a first load circuit, means defining a drift space following said first output resonator to permit bunching of the electrons therein in accordance with the velocity modulation imposed by the extraction of energy, a second output resonator having an excitation gap along said path following said drift space for extracting further energy therefrom in accordance With the velocity modulation thereof produced by the first output means, and means for coupling energy from said second output resonator to a second load circuit.

4. A high frequency amplifier having a cathode and a collector electrode having an electron stream path between them, means for applying a direct current potential for accelerating an electron stream along said path, an input resonator having an excitation gap said cathode and an apertured control electrode spaced along said stream from said cathode, means for supplying a high frequency input signal to said input resonator to 6 density modulate the electron stream by space charge control, a first output resonator having an excitation gap spaced further along said path and adjacent to said input resonator for extracting energy from said stream in accordance 'with the density modulation thereof and including an apertured accelerating electrode maintained at a positive direct current voltage with respect to said control electrode, means for coupling energy from said first output resonator to a desired load, means defining a drift space following said first output resonator to permit bunching of the electrons therein in accordance with the velocity modulation imposed by the extraction of energy, a second output resonator having an excitation gap along said path following said drift space for extracting further energy therefrom in accordance with the velocity modulation thereof produced by the first output means, and means for coupling energy from said second output resonator to said load.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,824 Hansen et a1. Apr. 28, 1942 2,375,223 Hansen et a1. May 8, 1945 2,423,968 Falk July 15, 1947 2,425,748 Llewellyn Aug. 19, 1947 2,442,662 Peterson June 1, 1948 2,469,843 Pierce May 10, 1949 2,493,046 Varian et al. Ian. 3, 1950 2,498,886 Hahn Feb. 28, 1950 2,579,480 Feenberg Dec. 25, 1951 2,595,698 Peter May 6, 1952 2,605,444 Garbung July 29, 1952 

